[CMAKE] Fix FindBerkeleyDB for FreeBSD
[CMAKE] Fix FindBerkeleyDB for FreeBSD

Summary:
The files are located under `/usr/local/<include|lib>/db5/` on FreeBSD 12.
Using `PATH_SUFFIXES` allow to search with the `db5` directory in the
path.

Test Plan:
On FreeBSD (tested on FreeBSD 12):
  cmake -GNinja -DBUILD_BITCOIN_QT=OFF ..
Check that cmake finds the library.

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4709

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